1. Field of the Invention
This invention relates generally to the fabrication of electronic components such as integrated circuit semiconductors and, in particular, to the cleaning of contaminates from the surface of substrates such as semiconductor wafers used to make the electronic component.
2. Description of Related Art
The fabrication of electronic components such as integrated circuit semiconductors is very exacting and complex and requires a number of processing steps requiring extreme precision to form the desired circuit pattern on the component substrate. Typical semiconductor devices now have circuit line widths typically less than 1 micron with close spacing of the lines and via interconnections. Contamination of the semiconductor substrate in the form of particles and/or films on the substrate may cause short circuits, open circuits and other defects which can cause the component to fail and/or adversely affect the performance of the component. For example, an individual particle as small as 100 angstroms in diameter can result in a killer defect in a modern microcircuit electronic component.
Cleaning the surface of the semiconductor substrate is therefore a critical step in integrated circuit fabrication and periodic cleaning of the substrate during the fabrication process is needed to maintain product integrity. There are currently numerous methods used to clean substrate surfaces in the electronic industry and basically solvents or chemical cleaning are used to remove contaminate particles and films from the surfaces. Chemical solutions are typically combined with megasonic or ultrasonic devices wherein the component to be cleaned is immersed in the chemical solution and the megasonic or ultrasonic devices used to impart high energy sonic waves to the surface of the component which in combination with the chemical solution removes organic films, ionic impurities and contaminate particles from the substrate surface.
A number of cleaning methods are described in U.S. Pat. No. 5,062,898, which patent is hereby incorporated by reference. For example, gas jet cleaning and liquid spray cleaning are used to clean relatively large particles from silicon wafers. Another cleaning technique involves the use of a carbon dioxide aerosol to xe2x80x9csand blastxe2x80x9d a contaminated surface. In this process, pressurized gaseous carbon dioxide is expanded in an outlet nozzle, and the resulting cooling forms solid carbon dioxide particles in the outlet stream which traverses the surface boundary layer of the substrate and strikes the contaminated surface. The technique of utilizing solid carbon dioxide to remove particulates from surfaces is noted therein. A number of other cleaning techniques using carbon dioxide are discussed in the patent.
A process for removing undesired sub-micron particles from a substrate is shown in U.S. Pat. No. 5,456,759 wherein the substrate to be cleaned is placed in a cleaning chamber provided with megasonic energy-producing means. A liquefied gas such as liquid carbon dioxide is introduced into the cleaning chamber and the substrate subjected to the liquid carbon dioxide agitated using megasonic energy. Another method for cleaning semiconductor wafers using liquefied gases is shown in U.S. Pat. No. 5,494,526 wherein a semiconductor is placed in a cleaning chamber and the liquefied gas cleaning agent changed to a vapor phase so that the cleaning agent penetrates the topography of the surface to be cleaned. The cleaning agent is then returned to the liquid phase in the cleaning chamber and finally flash-evaporated to complete the cleaning process. Megasonic units or exciters are provided to megasonically agitate the bath and the wafer semiconductor substrate in contact with the cleaning agent.
Another method for removing undesired materials from a substrate is shown in U.S. Pat. No. 5,316,591 wherein the contaminated substrate is placed in a cleaning chamber provided with cavitation-producing means. A liquefied gas such as liquid carbon dioxide is introduced into the cleaning chamber and the liquid carbon dioxide cavitated using a megasonic transducer.
All the above patents are hereby incorporated by reference.
Unfortunately, wafer contamination is still a problem in the semiconductor fabrication industry and as the industry advances and technology is being developed to form smaller and more complex circuits, a more effective and efficient cleaning method is required to produce semiconductor components.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for removing contaminating particles and/or films from a surface such as a substrate used to make electronic components such as semiconductors which method is efficient and effective to remove contaminating particles less than 0.1 micron from the substrate surface.
It is a further object of the present invention to provide an apparatus for removing contaminating particles and/or films from substrates used to make electronic components such as semiconductor wafers which apparatus is efficient and effective to remove contaminating particles less than 0.1 micron from the substrate surface.
It is another object of the present invention to provide electronic component substrates including semiconductor wafers which have been cleaned using the method and apparatus of the invention.
Another object of the invention is to provide electronic components made using electronic component substrates cleaned using the method and apparatus of the invention.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method for removing contaminating particles and/or films from a contaminating particle and/or film containing surface such as a semiconductor wafer comprising the steps of:
providing a liquefied gas in a distributor having an outlet nozzle;
imparting megasonic energy to the liquefied gas in the distributor thereby energizing the liquefied gas; and
directing the energized liquefied gas from the outlet nozzle of the distributor as a liquid stream onto the surface of the substrate having contaminating particles and/or films to remove the contaminating particles and/or films from the substrate surface to provide a cleaned substrate surface.
In another aspect of the present invention, an apparatus is provided for removing contaminating particles and/or films from a contaminating particle and/or film containing substrate surface such as a semiconductor wafer comprising:
distributor means for holding a supply of liquefied gas the distributor means having an outlet distribution nozzle;
megasonic energy forming means associated with the distributor means to energize the liquefied gas held in the distributor means;
wherein the energized liquefied gas is directed as a liquid from the outlet distribution nozzle to a substrate surface having contaminating particles and/or a film thereon so that the contaminating particles and/or film are removed from the substrate surface providing a cleaned substrate surface.
In another aspect of the present invention, the megasonically energized liquefied gas stream is directed onto the surface to be cleaned at an acute angle formed by the plane of the surface to be cleaned and the direction of the megasonically accuated liquefied gas being directed from the outlet distribution nozzle and impinging on the substrate surface. An acute angle between 30xc2x0 and 60xc2x0 is preferred.
In another aspect of the present invention, the method and apparatus of the invention may be employed to clean a variety of surfaces having contaminating particles and/or films such as circuit boards, medical instruments and optical lenses as well as semiconductor wafers and other substrates used in electronic component fabrication.